Trace ElementsTrace Elements

NoteNotemagnitudemagnitudeof of majormajorelementelementchangeschanges

Figure 8-2. Harker variation diagram for310 analyzed volcanic rocks from CraterLake (Mt. Mazama), Oregon Cascades.Data compiled by Rick Conrey (personalcommunication). From Winter (2001) AnFrom Winter (2001) AnIntroduction to Igneous and MetamorphicIntroduction to Igneous and MetamorphicPetrology. Prentice Hall.Petrology. Prentice Hall.

wt %

wt %

Figure 9-1.Figure 9-1. Harker Diagram for Crater Lake. From data Harker Diagram for Crater Lake. From datacompiled by Rick compiled by Rick ConreyConrey. From Winter (2001) An Introduction. From Winter (2001) An Introductionto Igneous and Metamorphic Petrology. Prentice Hall.to Igneous and Metamorphic Petrology. Prentice Hall.

NoteNotemagnitudemagnitudeof of tracetraceelementelementchangeschanges

Trace ElementsTrace Elements

ppm

ppm

ppm

ppm

Element DistributionElement DistributionGoldschmidtGoldschmidt’’s rules (simplistic, but useful)s rules (simplistic, but useful)

1.1. Two ions with the same valence and radiusTwo ions with the same valence and radiusshould exchange easily and enter a solidshould exchange easily and enter a solidsolution in amounts equal to their overallsolution in amounts equal to their overallproportionsproportions

How does Rb behave? Ni?How does Rb behave? Ni?

GoldschmidtGoldschmidt’’s ruless rules2. If two ions have a similar radius and the same2. If two ions have a similar radius and the same

valence: the smaller ion is preferentially incorporatedvalence: the smaller ion is preferentially incorporatedinto the solid over the liquidinto the solid over the liquid

Fig. 6-10. Isobaric T-X phasediagram at atmosphericpressure After Bowen andShairer (1932), Amer. J. Sci. 5thSer., 24, 177-213. From WinterFrom Winter(2001) An Introduction to(2001) An Introduction toIgneous and MetamorphicIgneous and MetamorphicPetrology. Prentice Hall.Petrology. Prentice Hall.

Relative ionic radii for common valencesand coordination numbers

Preference forPreference formineral phasemineral phase

PreferencePreferencefor meltfor melt

Plot of ionic radius vs. ionic charge fortrace elements of geological interest.Ionic radii are quoted for eight-foldcoordination to allow for comparisonbetween elements. From Rollinson(1993).

Ionic chargeIonic chargevs. radiusvs. radius

3. If two ions have a similar radius, but differentvalence: the ion with the higher charge ispreferentially incorporated into the solid over theliquid

Chemical FractionationChemical Fractionation

The uneven distribution of an ion betweenThe uneven distribution of an ion betweentwo competing (equilibrium) phasestwo competing (equilibrium) phases

Exchange equilibrium of a Exchange equilibrium of a componentcomponent ii betweenbetweentwo two phasesphases (solid and liquid) (solid and liquid)

ii (liquid)(liquid) = = ii (solid)(solid)

KKDD = = = =

K =K = equilibrium constantequilibrium constant

a a solidsolid

a a liquidliquidii

ii

γγ XX solidsolid

γγ XX liquidliquidii

ii

ii

ii

Trace element concentrations are in theTrace element concentrations are in theHenryHenry’’s Law region of concentration, sos Law region of concentration, sotheir activity varies in direct relation to theirtheir activity varies in direct relation to theirconcentration in the system, where [a] = (c)concentration in the system, where [a] = (c)

Thus if Thus if XXNiNi in the system doubles the in the system doubles the XXNiNi ininall all phases will doublephases will double This does not mean that This does not mean that XXNiNi in all phasesin all phases

is the same, since trace elements dois the same, since trace elements dofractionate. Rather the fractionate. Rather the XXNiNi within eachwithin eachphase will vary in proportion to thephase will vary in proportion to thesystem concentrationsystem concentration

incompatibleincompatible elements are concentrated in the elements are concentrated in themeltmelt

(K(KDD or D) or D) «« 1 1

compatiblecompatible elements are concentrated in the elements are concentrated in thesolidsolid

KKDD or D or D »» 1 1

where D is the partition coefficient for any given trace where D is the partition coefficient for any given trace element between phases; D is a constant for dilute element between phases; D is a constant for dilute concentrations of elementsconcentrations of elements

For dilute solutions can substitute D for KFor dilute solutions can substitute D for KDD::

D =D =

Where CWhere CSS = the concentration of some element in = the concentration of some element inthe solid phasethe solid phase

CCSSCCLL

IncompatibleIncompatible elements commonly elements commonly →→ two subgroups two subgroups

Smaller, highly charged Smaller, highly charged high field strength (HFS)high field strength (HFS)elementselements (REE, Th, U, Ce, Pb(REE, Th, U, Ce, Pb4+4+, Zr, Hf, Ti, Nb,, Zr, Hf, Ti, Nb,Ta)Ta)

Low field strength Low field strength large ion lithophile (LIL)large ion lithophile (LIL)elements elements (K, Rb, Cs, Ba, Pb(K, Rb, Cs, Ba, Pb2+2+, Sr, Eu, Sr, Eu2+2+)) are more are moremobile, particularly if a fluid phase is involvedmobile, particularly if a fluid phase is involved

High field strength (HFS) elementsHigh field strength (HFS) elementsSmaller, highly chargedSmaller, highly charged

Large Ion Large Ion Lithophiles Lithophiles ((LILsLILs))Low field strength (large ions, Low field strength (large ions, lower charge), more mobilelower charge), more mobile

Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace Elements in Basaltic and Andesitic Rocks

Olivine Opx Cpx Garnet Plag Amph MagnetiteRb 0.010 0.022 0.031 0.042 0.071 0.29 Sr 0.014 0.040 0.060 0.012 1.830 0.46 Ba 0.010 0.013 0.026 0.023 0.23 0.42 Ni 14 5 7 0.955 0.01 6.8 29Cr 0.70 10 34 1.345 0.01 2.00 7.4La 0.007 0.03 0.056 0.001 0.148 0.544 2Ce 0.006 0.02 0.092 0.007 0.082 0.843 2Nd 0.006 0.03 0.230 0.026 0.055 1.340 2Sm 0.007 0.05 0.445 0.102 0.039 1.804 1Eu 0.007 0.05 0.474 0.243 0.1/1.5* 1.557 1Dy 0.013 0.15 0.582 1.940 0.023 2.024 1Er 0.026 0.23 0.583 4.700 0.020 1.740 1.5Yb 0.049 0.34 0.542 6.167 0.023 1.642 1.4Lu 0.045 0.42 0.506 6.950 0.019 1.563Data from Rollinson (1993). * Eu3+/Eu2+ Italics are estimated

Rar

e Ea

rth E

lem

ents

Compatibility depends on minerals and melts involved.Compatibility depends on minerals and melts involved.

Which are incompatible? Why?Which are incompatible? Why?

For a For a rock,rock, determine the determine the bulk distributionbulk distributioncoefficient Dcoefficient D for an element by calculating for an element by calculatingthe contribution for each mineralthe contribution for each mineral

DDii = = ΣΣ W WAA DDiAiA

WWAA = weight % of mineral A in the rock = weight % of mineral A in the rock

DDii = partition coefficient of element i in = partition coefficient of element i in mineral Amineral A

AA

AA

Example: hypothetical garnet lherzolite = 60% olivine, 25%Example: hypothetical garnet lherzolite = 60% olivine, 25%orthopyroxene, 10% clinopyroxene, and 5% garnet (all by orthopyroxene, 10% clinopyroxene, and 5% garnet (all by weightweight),),using the data in Table 9-1, is:using the data in Table 9-1, is:

DDErEr = (0.6 = (0.6 ·· 0.026) + (0.25 0.026) + (0.25 ·· 0.23) + (0.10 0.23) + (0.10 ·· 0.583) + (0.05 0.583) + (0.05 ·· 4.7) = 4.7) = 0.3660.366

Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace Elements in Basaltic and Andesitic Rocks

Olivine Opx Cpx Garnet Plag Amph MagnetiteRb 0.010 0.022 0.031 0.042 0.071 0.29 Sr 0.014 0.040 0.060 0.012 1.830 0.46 Ba 0.010 0.013 0.026 0.023 0.23 0.42 Ni 14 5 7 0.955 0.01 6.8 29Cr 0.70 10 34 1.345 0.01 2.00 7.4La 0.007 0.03 0.056 0.001 0.148 0.544 2Ce 0.006 0.02 0.092 0.007 0.082 0.843 2Nd 0.006 0.03 0.230 0.026 0.055 1.340 2Sm 0.007 0.05 0.445 0.102 0.039 1.804 1Eu 0.007 0.05 0.474 0.243 0.1/1.5* 1.557 1Dy 0.013 0.15 0.582 1.940 0.023 2.024 1Er 0.026 0.23 0.583 4.700 0.020 1.740 1.5Yb 0.049 0.34 0.542 6.167 0.023 1.642 1.4Lu 0.045 0.42 0.506 6.950 0.019 1.563Data from Rollinson (1993). * Eu3+/Eu2+ Italics are estimated

Rar

e Ea

rth E

lem

ents

Trace elements strongly partitioned into a single mineralTrace elements strongly partitioned into a single mineral Ni - olivine = 14Ni - olivine = 14

Figure 9-1a.Figure 9-1a. Ni Harker Diagram for Crater Lake. From data compiled by Rick Ni Harker Diagram for Crater Lake. From data compiled by Rick ConreyConrey. From. FromWinter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Incompatible trace elements concentrate Incompatible trace elements concentrate →→ liquid liquid

Reflect the proportion of liquid at a given state ofReflect the proportion of liquid at a given state ofcrystallization or meltingcrystallization or melting

Figure 9-1b.Figure 9-1b. Zr Harker Diagram for Crater Lake. From data compiled by Rick Zr Harker Diagram for Crater Lake. From data compiled by Rick ConreyConrey..From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Trace Element BehaviorTrace Element Behavior The concentration of a The concentration of a majormajor element in a phase is element in a phase is

usually buffered by the system, so that it variesusually buffered by the system, so that it varieslittle in a phase as the system composition changeslittle in a phase as the system composition changes

At a given T we could varyAt a given T we could varyXXmeltmelt from 20 from 20 →→ 60 % 60 %Mg/Fe without changing theMg/Fe without changing thecomposition of the melt orcomposition of the melt orthe olivinethe olivine

Trace elementTrace element concentrations are in theconcentrations are in theHenryHenry’’s Law region of concentration, sos Law region of concentration, sotheir activity varies in direct relation to theirtheir activity varies in direct relation to theirconcentration in the systemconcentration in the system

Trace element concentrations are in theTrace element concentrations are in theHenryHenry’’s Law region of concentration, sos Law region of concentration, sotheir activity varies in direct relation to theirtheir activity varies in direct relation to theirconcentration in the systemconcentration in the system

Thus if Thus if XXNiNi in the system doubles the in the system doubles the XXNiNi ininall phases will doubleall phases will double

Trace element concentrations are in theTrace element concentrations are in theHenryHenry’’s Law region of concentration, sos Law region of concentration, sotheir activity varies in direct relation to theirtheir activity varies in direct relation to theirconcentration in the systemconcentration in the system

Thus if Thus if XXNiNi in the system doubles the in the system doubles the XXNiNi ininall all phases will doublephases will double

Because of this, the Because of this, the ratiosratios of trace elements of trace elementsare often superior to the concentration of aare often superior to the concentration of asingle element in identifying the role of asingle element in identifying the role of aspecific mineralspecific mineral

K/RbK/Rb often used often used →→ the importance of the importance of amphiboleamphibole in a source rock in a source rock K & Rb behave very similarly, so K & Rb behave very similarly, so K/Rb should be ~ constantK/Rb should be ~ constant If amphibole, almost all K and Rb reside in itIf amphibole, almost all K and Rb reside in it Amphibole has a D of about 1.0 for K and 0.3 for RbAmphibole has a D of about 1.0 for K and 0.3 for Rb

Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace Elements in Basaltic and Andesitic Rocks

Olivine Opx Cpx Garnet Plag Amph MagnetiteRb 0.010 0.022 0.031 0.042 0.071 0.29 Sr 0.014 0.040 0.060 0.012 1.830 0.46 Ba 0.010 0.013 0.026 0.023 0.23 0.42 Ni 14 5 7 0.955 0.01 6.8 29Cr 0.70 10 34 1.345 0.01 2.00 7.4La 0.007 0.03 0.056 0.001 0.148 0.544 2Ce 0.006 0.02 0.092 0.007 0.082 0.843 2Nd 0.006 0.03 0.230 0.026 0.055 1.340 2Sm 0.007 0.05 0.445 0.102 0.039 1.804 1Eu 0.007 0.05 0.474 0.243 0.1/1.5* 1.557 1Dy 0.013 0.15 0.582 1.940 0.023 2.024 1Er 0.026 0.23 0.583 4.700 0.020 1.740 1.5Yb 0.049 0.34 0.542 6.167 0.023 1.642 1.4Lu 0.045 0.42 0.506 6.950 0.019 1.563Data from Rollinson (1993). * Eu3+/Eu2+ Italics are estimated

Rar

e Ea

rth E

lem

ents

Sr and Ba (also Sr and Ba (also incompatibleincompatible elements) elements) SrSr is excluded from most common minerals is excluded from most common minerals

except except plagioclaseplagioclase BaBa similarly excluded except in similarly excluded except in alkali feldsparalkali feldspar

Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace Elements in Basaltic and Andesitic Rocks

Olivine Opx Cpx Garnet Plag Amph MagnetiteRb 0.010 0.022 0.031 0.042 0.071 0.29 Sr 0.014 0.040 0.060 0.012 1.830 0.46 Ba 0.010 0.013 0.026 0.023 0.23 0.42 Ni 14 5 7 0.955 0.01 6.8 29Cr 0.70 10 34 1.345 0.01 2.00 7.4La 0.007 0.03 0.056 0.001 0.148 0.544 2Ce 0.006 0.02 0.092 0.007 0.082 0.843 2Nd 0.006 0.03 0.230 0.026 0.055 1.340 2Sm 0.007 0.05 0.445 0.102 0.039 1.804 1Eu 0.007 0.05 0.474 0.243 0.1/1.5* 1.557 1Dy 0.013 0.15 0.582 1.940 0.023 2.024 1Er 0.026 0.23 0.583 4.700 0.020 1.740 1.5Yb 0.049 0.34 0.542 6.167 0.023 1.642 1.4Lu 0.045 0.42 0.506 6.950 0.019 1.563Data from Rollinson (1993). * Eu3+/Eu2+ Italics are estimated

Rar

e Ea

rth E

lem

ents

CompatibleCompatible example: example: NiNi strongly fractionated strongly fractionated →→ olivineolivine > pyroxene > pyroxene CrCr and and ScSc →→ pyroxenespyroxenes »» olivine olivine Ni/Cr or Ni/Sc can distinguish the effects of olivineNi/Cr or Ni/Sc can distinguish the effects of olivine

and augite in a partial melt or a suite of rocksand augite in a partial melt or a suite of rocksproduced by fractional crystallizationproduced by fractional crystallization

Table 9-1. Partition Coefficients (CS/CL) for Some Commonly Used Trace Elements in Basaltic and Andesitic Rocks

Olivine Opx Cpx Garnet Plag Amph MagnetiteRb 0.010 0.022 0.031 0.042 0.071 0.29 Sr 0.014 0.040 0.060 0.012 1.830 0.46 Ba 0.010 0.013 0.026 0.023 0.23 0.42 Ni 14 5 7 0.955 0.01 6.8 29Cr 0.70 10 34 1.345 0.01 2.00 7.4La 0.007 0.03 0.056 0.001 0.148 0.544 2Ce 0.006 0.02 0.092 0.007 0.082 0.843 2Nd 0.006 0.03 0.230 0.026 0.055 1.340 2Sm 0.007 0.05 0.445 0.102 0.039 1.804 1Eu 0.007 0.05 0.474 0.243 0.1/1.5* 1.557 1Dy 0.013 0.15 0.582 1.940 0.023 2.024 1Er 0.026 0.23 0.583 4.700 0.020 1.740 1.5Yb 0.049 0.34 0.542 6.167 0.023 1.642 1.4Lu 0.045 0.42 0.506 6.950 0.019 1.563Data from Rollinson (1993). * Eu3+/Eu2+ Italics are estimated

Rar

e Ea

rth E

lem

ents

Models of Magma EvolutionModels of Magma Evolution Batch MeltingBatch Melting

The melt remains resident until at some point it isThe melt remains resident until at some point it isreleased and moves upwardreleased and moves upward

Equilibrium melting process with variable %Equilibrium melting process with variable %meltingmelting

Models of Magma EvolutionModels of Magma Evolution Batch MeltingBatch Melting

CCLL = trace element concentration in the liquid = trace element concentration in the liquidCCOO = trace element concentration in the original rock = trace element concentration in the original rock

before melting beganbefore melting beganF = wt fraction of melt F = wt fraction of melt producedproduced = melt/(melt + rock) = melt/(melt + rock)

CCCC

11DDii(1(1 F)F) FF

LL

OO==

−− ++

Batch MeltingBatch Melting A plot of CA plot of CLL/C/COO vs. F for various vs. F for various

values of Dvalues of Dii using the using theprevious equationprevious equation

DDii = 1.0 = 1.0

Figure 9-2.Figure 9-2. Variation in the relative concentration of a Variation in the relative concentration of atrace element in a liquid vs. source rock as a trace element in a liquid vs. source rock as a fiunctionfiunctionof D and the fraction melted, using equation (9-5) forof D and the fraction melted, using equation (9-5) forequilibrium batch melting. From Winter (2001) Anequilibrium batch melting. From Winter (2001) AnIntroduction to Igneous and Metamorphic Petrology.Introduction to Igneous and Metamorphic Petrology.Prentice Hall.Prentice Hall.

DDii »» 1.0 ( 1.0 (compatible compatible element)element)

Very low concentration inVery low concentration inmeltmelt

Especially for low %Especially for low %melting (low F)melting (low F)

Figure 9-2.Figure 9-2. Variation in the relative concentration of a Variation in the relative concentration of atrace element in a liquid vs. source rock as a trace element in a liquid vs. source rock as a fiunctionfiunctionof D and the fraction melted, using equation (9-5) forof D and the fraction melted, using equation (9-5) forequilibrium batch melting. From Winter (2001) Anequilibrium batch melting. From Winter (2001) AnIntroduction to Igneous and Metamorphic Petrology.Introduction to Igneous and Metamorphic Petrology.Prentice Hall.Prentice Hall.

Highly Highly incompatibleincompatible elements elements•• Greatly concentrated in theGreatly concentrated in the

initial small fraction of meltinitial small fraction of meltproduced by partial meltingproduced by partial melting

•• Subsequently diluted as F Subsequently diluted as Fincreasesincreases

Figure 9-2.Figure 9-2. Variation in the relative concentration of a Variation in the relative concentration of atrace element in a liquid vs. source rock as a trace element in a liquid vs. source rock as a fiunctionfiunctionof D and the fraction melted, using equation (9-5) forof D and the fraction melted, using equation (9-5) forequilibrium batch melting. From Winter (2001) Anequilibrium batch melting. From Winter (2001) AnIntroduction to Igneous and Metamorphic Petrology.Introduction to Igneous and Metamorphic Petrology.Prentice Hall.Prentice Hall.

As F As F →→ 1 the concentration of 1 the concentration ofeveryevery trace element in the liquid trace element in the liquid= the source rock (C= the source rock (CLL/C/COO→→ 1) 1)

As F As F →→ 1 1CCLL/C/COO →→ 1 1

CC

1Di(1 F) F

L

O

=− +

Figure 9-2.Figure 9-2. Variation in the relative concentration of a Variation in the relative concentration of atrace element in a liquid vs. source rock as a trace element in a liquid vs. source rock as a fiunctionfiunctionof D and the fraction melted, using equation (9-5) forof D and the fraction melted, using equation (9-5) forequilibrium batch melting. From Winter (2001) Anequilibrium batch melting. From Winter (2001) AnIntroduction to Igneous and Metamorphic Petrology.Introduction to Igneous and Metamorphic Petrology.Prentice Hall.Prentice Hall.

As F As F →→ 0 0 CCLL/C/COO →→ 1/D 1/Dii

If we know CIf we know CLL of a magma derived of a magma derivedby a small degree of batch melting,by a small degree of batch melting,and we know Dand we know Dii we can estimate we can estimatethe concentration of that element inthe concentration of that element inthe source region (Cthe source region (COO))

CC

1Di(1 F) F

L

O

=− +

Figure 9-2.Figure 9-2. Variation in the relative concentration of a Variation in the relative concentration of atrace element in a liquid vs. source rock as a trace element in a liquid vs. source rock as a fiunctionfiunctionof D and the fraction melted, using equation (9-5) forof D and the fraction melted, using equation (9-5) forequilibrium batch melting. From Winter (2001) Anequilibrium batch melting. From Winter (2001) AnIntroduction to Igneous and Metamorphic Petrology.Introduction to Igneous and Metamorphic Petrology.Prentice Hall.Prentice Hall.

For very For very incompatibleincompatible elements as D elements as Dii →→ 0 0

reduces to:reduces to:

CC

1F

L

O

=

CC

1Di (1 F) F

L

O

=− +

If we know the concentration of a veryIf we know the concentration of a veryincompatible element in both a magma and theincompatible element in both a magma and thesource rock, we can determine the fraction ofsource rock, we can determine the fraction ofpartial melt producedpartial melt produced

Worked Example of Batch Melting: Worked Example of Batch Melting: Rb and SrRb and SrBasalt with the mode:Basalt with the mode:

1.1. Convert to Convert to weightweight % minerals ( % minerals (WWolol W Wcpxcpx etc.)etc.)

Table 9-2. Conversion from mode toweight percent

Mineral Mode Density Wt prop Wt%ol 15 3.6 54 0.18cpx 33 3.4 112.2 0.37plag 51 2.7 137.7 0.45

Sum 303.9 1.00

Worked Example of Batch Melting: Worked Example of Batch Melting: Rb and SrRb and Sr

Table 9-2. Conversion from mode toweight percent

Mineral Mode Density Wt prop Wt%ol 15 3.6 54 0.18cpx 33 3.4 112.2 0.37plag 51 2.7 137.7 0.45

Sum 303.9 1.00

Basalt with the mode:Basalt with the mode:

1.1. Convert to Convert to weightweight % minerals ( % minerals (WWolol W Wcpxcpx etc.)etc.)

2.2. Use: Use: DDii = = ΣΣ W WAA D Dii

and the table of D values for Rb and Sr in each mineraland the table of D values for Rb and Sr in each mineralto calculate the bulk distribution coefficients: to calculate the bulk distribution coefficients: DDRbRb ==0.045 and 0.045 and DDSrSr = 0.848= 0.848

Table 9-3 . Batch Fractionation Model for Rb and Sr

CL/CO = 1/(D(1-F)+F)DRb DSr

F 0.045 0.848 Rb/Sr0.05 9.35 1.14 8.190.1 6.49 1.13 5.730.15 4.98 1.12 4.430.2 4.03 1.12 3.610.3 2.92 1.10 2.660.4 2.29 1.08 2.110.5 1.89 1.07 1.760.6 1.60 1.05 1.520.7 1.39 1.04 1.340.8 1.23 1.03 1.200.9 1.10 1.01 1.09

3.3. Use the batch melting equation to calculate C Use the batch melting equation to calculate CLL/C/COOfor various values of Ffor various values of F

From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

4.4. Plot C Plot CLL/C/COO vs. F for each element vs. F for each element

Figure 9-3.Figure 9-3. Change in the concentration Change in the concentrationof Rb and Sr in the melt derived byof Rb and Sr in the melt derived byprogressive batch melting of a basalticprogressive batch melting of a basalticrock consisting of plagioclase, augite,rock consisting of plagioclase, augite,and olivine. From Winter (2001) Anand olivine. From Winter (2001) AnIntroduction to Igneous andIntroduction to Igneous andMetamorphic Petrology. Prentice Hall.Metamorphic Petrology. Prentice Hall.

Incremental Batch MeltingIncremental Batch Melting

Calculate batch melting for successiveCalculate batch melting for successivebatches (same equation)batches (same equation)

Must recalculate DMust recalculate Dii as solids change as as solids change asminerals are minerals are selectivelyselectively melted (computer) melted (computer)

Fractional CrystallizationFractional Crystallization1. Crystals remain in equilibrium with each1. Crystals remain in equilibrium with each

melt incrementmelt increment

Rayleigh fractionationRayleigh fractionation The other extreme: separation of eachThe other extreme: separation of each

crystal as it formed = perfectly continuouscrystal as it formed = perfectly continuousfractional crystallization in a magmafractional crystallization in a magmachamberchamber

Rayleigh fractionationRayleigh fractionation The other extreme: separation of each The other extreme: separation of each

crystal as it formed = perfectly continuouscrystal as it formed = perfectly continuousfractional crystallization in a magmafractional crystallization in a magmachamberchamber Concentration of some element in the Concentration of some element in the residualresidual

liquid, Cliquid, CLL is modeled by the Rayleigh is modeled by the Rayleighequation:equation:

CCLL/C/COO = F = F (D -1)(D -1) Rayleigh FractionationRayleigh Fractionation

Other models are used to analyzeOther models are used to analyze Mixing of magmasMixing of magmas Wall-rock assimilationWall-rock assimilation Zone refiningZone refining Combinations of processesCombinations of processes

The Rare Earth Elements (REE)The Rare Earth Elements (REE)

Contrasts and similarities in the D values:Contrasts and similarities in the D values:All are incompatibleAll are incompatible

Table 9-1 . Partition Coefficients for some commonly used trace elements in basaltic and andesitic rocks Bulk D calculation

Olivine Opx Cpx Garnet Plag AmphRb 0.006 0.02 0.04 0.001 0.1 0.3Sr 0.01 0.01 0.14 0.001 1.8 0.57Ba 0.006 0.12 0.07 0.002 0.23 0.31Ni 14 5 2.6 0.4 0.01 3Cr 2.1 10 8.4 0.17 10 1.6La 0.007 0.02 0.08 0.05 0.14 0.27Ce 0.009 0.02 0.34 0.05 0.14 0.34Nd 0.009 0.05 0.6 0.07 0.08 0.19Sm 0.009 0.05 0.9 0.06 0.08 0.91Eu 0.008 0.05 0.9 0.9 0.1/1.5* 1.01Tb 0.01 0.05 1 5.6 0.03 1.4Er 0.013 0.31 1 18 0.08 0.48Yb 0.014 0.34 0.2 30 0.07 0.97Lu 0.016 0.11 0.82 35 0.08 0.89data from Henderson (1982) * Eu3+/Eu2+ Italics are estimated

Rar

e E

arth

Ele

men

ts

Also Note:Also Note:

HREEHREE are less are lessincompatibleincompatible

Especially in Especially ingarnetgarnet

EuEu can can →→ 2+ 2+which conc.which conc.in in plagioclaseplagioclase

REE DiagramsREE DiagramsPlots of concentration as the ordinate (y-axis)Plots of concentration as the ordinate (y-axis)

against increasing atomic numberagainst increasing atomic number Degree of compatibility increases from leftDegree of compatibility increases from left

to right across the diagramto right across the diagram

Con

cent

ratio

nC

once

ntra

tion

La Ce Nd Sm Eu Tb ErLa Ce Nd Sm Eu Tb Er Dy Dy Yb LuYb Lu

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

0 10 20 30 40 50 60 70 80 90 100

Atomic Number (Z)

Log

(Abu

ndan

ce in

CI C

hond

ritic

Met

eorit

e)

HHe

Li

Be

B

C

N

O

FSc

FeNi

Ne MgSiS

CaAr

Ti

PbPtSn BaV

K

NaAlPCl

ThU

Eliminate Eliminate Oddo-Harkins effectOddo-Harkins effect and make y-scale and make y-scalemore functional by normalizing to a standardmore functional by normalizing to a standard estimates of primordial mantle REEestimates of primordial mantle REE chondrite meteorite concentrationschondrite meteorite concentrations

What would an REE diagram lookWhat would an REE diagram looklike for an analysis of a chondritelike for an analysis of a chondrite

meteorite?meteorite?

0.00

2.00

4.00

6.00

8.00

10.00

56 58 60 62 64 66 68 70 72

sam

ple/

chon

drite

L La Ce Nd Sm Eu Tb Er Yb Lu

?

Divide each element in analysis by theDivide each element in analysis by theconcentration in a chondrite standardconcentration in a chondrite standard

0.00

2.00

4.00

6.00

8.00

10.00

56 58 60 62 64 66 68 70 72

sam

ple/

chon

drite

L La Ce Nd Sm Eu Tb Er Yb Lu

REE diagrams using batch melting model ofREE diagrams using batch melting model ofa garnet lherzolite for various values of F:a garnet lherzolite for various values of F:

Figure 9-4.Figure 9-4. Rare Earth Rare Earthconcentrations (normalized toconcentrations (normalized tochondrite) for melts produced atchondrite) for melts produced atvarious values of F via melting of avarious values of F via melting of ahypothetical garnet lherzolite usinghypothetical garnet lherzolite usingthe batch melting model (equationthe batch melting model (equation9-5). From Winter (2001) An9-5). From Winter (2001) AnIntroduction to Igneous andIntroduction to Igneous andMetamorphic Petrology. PrenticeMetamorphic Petrology. PrenticeHall.Hall.

Europium anomalyEuropium anomaly when plagioclase is when plagioclase is a fractionating phenocrysta fractionating phenocryst

oror a residual solid in sourcea residual solid in source

Figure 9-5.Figure 9-5. REE diagram for 10% REE diagram for 10%batch melting of a hypotheticalbatch melting of a hypotheticallherzolite with 20% plagioclase,lherzolite with 20% plagioclase,resulting in a pronounced negativeresulting in a pronounced negativeEuropium anomaly. From WinterEuropium anomaly. From Winter(2001) An Introduction to Igneous(2001) An Introduction to Igneousand Metamorphic Petrology.and Metamorphic Petrology.Prentice Hall.Prentice Hall.

Spider DiagramsSpider DiagramsAn extension of the normalized REEAn extension of the normalized REEtechnique to a broader spectrum of elementstechnique to a broader spectrum of elements

Fig. 9-6. Spider diagram for an alkaline basalt from Gough Island, southern Atlantic.After Sun and MacDonough (1989). In A. D. Saunders and M. J. Norry (eds.),Magmatism in the Ocean Basins. Geol. Soc. London Spec. Publ., 42. pp. 313-345.

Chondrite-normalized spiderChondrite-normalized spiderdiagrams are commonlydiagrams are commonlyorganized by (the authororganized by (the author’’ssestimate) of increasingestimate) of increasingincompatibility L incompatibility L ←← R R

Different estimates Different estimates →→different ordering (poordifferent ordering (poorstandardization)standardization)

MORB-normalized SpiderMORB-normalized SpiderSeparates LIL and HFSSeparates LIL and HFS

Figure 9-7.Figure 9-7. Ocean island basalt Ocean island basaltplotted on a mid-ocean ridgeplotted on a mid-ocean ridgebasalt (MORB) normalizedbasalt (MORB) normalizedspider diagram of the type usedspider diagram of the type usedby Pearce (1983). Data fromby Pearce (1983). Data fromSun and McDonough (1989).Sun and McDonough (1989).From Winter (2001) AnFrom Winter (2001) AnIntroduction to Igneous andIntroduction to Igneous andMetamorphic Petrology.Metamorphic Petrology.Prentice Hall.Prentice Hall.

Application of Trace Elements toIgneous Systems

1. Use like major elements on variation diagrams to1. Use like major elements on variation diagrams todocument FX, assimilation, etc. in a suite of rocksdocument FX, assimilation, etc. in a suite of rocks More sensitive More sensitive →→ larger variations as process larger variations as process

continuescontinues

Figure 9-1a.Figure 9-1a. Ni Harker Diagram for Ni Harker Diagram forCrater Lake. From data compiled byCrater Lake. From data compiled byRick Rick ConreyConrey. From Winter (2001) An. From Winter (2001) AnIntroduction to Igneous andIntroduction to Igneous andMetamorphic Petrology. Prentice Hall.Metamorphic Petrology. Prentice Hall.

2. Identification of the source rock or a particular2. Identification of the source rock or a particularmineral involved in either partial melting ormineral involved in either partial melting orfractional crystallization processesfractional crystallization processes

Table 9-1 . Partition Coefficients for some commonly used trace elements in basaltic and andesitic rocks Bulk D calculation

Olivine Opx Cpx Garnet Plag AmphRb 0.006 0.02 0.04 0.001 0.1 0.3Sr 0.01 0.01 0.14 0.001 1.8 0.57Ba 0.006 0.12 0.07 0.002 0.23 0.31Ni 14 5 2.6 0.4 0.01 3Cr 2.1 10 8.4 0.17 10 1.6La 0.007 0.02 0.08 0.05 0.14 0.27Ce 0.009 0.02 0.34 0.05 0.14 0.34Nd 0.009 0.05 0.6 0.07 0.08 0.19Sm 0.009 0.05 0.9 0.06 0.08 0.91Eu 0.008 0.05 0.9 0.9 0.1/1.5* 1.01Tb 0.01 0.05 1 5.6 0.03 1.4Er 0.013 0.31 1 18 0.08 0.48Yb 0.014 0.34 0.2 30 0.07 0.97Lu 0.016 0.11 0.82 35 0.08 0.89data from Henderson (1982) * Eu3+/Eu2+ Italics are estimated

Rar

e E

arth

Ele

men

ts

GarnetGarnet concentrates the HREE and fractionates among them concentrates the HREE and fractionates among them

Thus if garnet is in equilibrium with the partial melt (a residualThus if garnet is in equilibrium with the partial melt (a residualphase in the source left behind) expect a steep (-) slope in REE phase in the source left behind) expect a steep (-) slope in REE andandHREEHREE

Shallow (< 40Shallow (< 40km) partialkm) partialmelting of themelting of themantle will havemantle will haveplagioclaseplagioclase in inthe the resuduumresuduumand a Euand a Euanomaly willanomaly willresultresult

0.00

2.00

4.00

6.00

8.00

10.00

56 58 60 62 64 66 68 70 72

sam

ple/

chon

drite

La Ce Nd Sm Eu Tb Er Yb Lu

67% Ol 17% Opx 17% Cpx

0.00

2.00

4.00

6.00

8.00

10.00

56 58 60 62 64 66 68 70 72

sam

ple/

chon

drite

La Ce Nd Sm Eu Tb Er Yb Lu

57% Ol 14% Opx 14% Cpx 14% Grt

Garnet and Plagioclaseeffect on HREE

0.00

2.00

4.00

6.00

8.00

10.00

sam

ple/

chon

drite

60% Ol 15% Opx 15% Cpx 10%Plag

La Ce Nd Sm Eu Tb Er Yb Lu

Figure 9-3.Figure 9-3. Change in the concentration Change in the concentrationof Rb and Sr in the melt derived byof Rb and Sr in the melt derived byprogressive batch melting of a basalticprogressive batch melting of a basalticrock consisting of plagioclase, augite,rock consisting of plagioclase, augite,and olivine. From Winter (2001) Anand olivine. From Winter (2001) AnIntroduction to Igneous andIntroduction to Igneous andMetamorphic Petrology. Prentice Hall.Metamorphic Petrology. Prentice Hall.

Table 9-6 A brief summary of some particularly useful trace elements in igneous petrology

Element Use as a petrogenetic indicator

Ni, Co, Cr Highly compatible elements. Ni (and Co) are concentrated in olivine, and Cr in spinel andclinopyroxene. High concentrations indicate a mantle source.

V, Ti Both show strong fractionation into Fe-Ti oxides (ilmenite or titanomagnetite). If they behavedifferently, Ti probably fractionates into an accessory phase, such as sphene or rutile.

Zr, Hf Very incompatible elements that do not substitute into major silicate phases (although they mayreplace Ti in sphene or rutile).

Ba, Rb Incompatible element that substitutes for K in K-feldspar, micas, or hornblende. Rb substitutesless readily in hornblende than K-spar and micas, such that the K/Ba ratio may distinguish thesephases.

Sr Substitutes for Ca in plagioclase (but not in pyroxene), and, to a lesser extent, for K in K-feldspar. Behaves as a compatible element at low pressure where plagioclase forms early, butas an incompatible at higher pressure where plagioclase is no longer stable.

REE Garnet accommodates the HREE more than the LREE, and orthopyroxene and hornblende doso to a lesser degree. Sphene and plagioclase accommodates more LREE. Eu2+ is stronglypartitioned into plagioclase.

Y Commonly incompatible (like HREE). Strongly partitioned into garnet and amphibole. Spheneand apatite also concentrate Y, so the presence of these as accessories could have asignificant effect.

Table 9-6.Table 9-6. After Green (1980). After Green (1980). TectonophysTectonophys., ., 6363, 367-385. From Winter (2001) An Introduction to Igneous and, 367-385. From Winter (2001) An Introduction to Igneous andMetamorphic Petrology. Prentice Hall.Metamorphic Petrology. Prentice Hall.

Trace elements as a tool toTrace elements as a tool todetermine determine paleotectonicpaleotectonic

environmentenvironment Useful for rocks in mobile belts that are noUseful for rocks in mobile belts that are no

longer recognizably in their original settinglonger recognizably in their original setting Can trace elements be discriminators ofCan trace elements be discriminators of

igneous environment?igneous environment? Approach is Approach is empiricalempirical on on modernmodern occurrences occurrences Concentrate on elements that are immobileConcentrate on elements that are immobile

during low/medium grade metamorphismduring low/medium grade metamorphism

Figure 9-8.Figure 9-8. (a)(a) after Pearce and after Pearce and Cann Cann (1973), (1973), Earth Planet, Sci. Earth Planet, Sci. LettLett., ., 1919, 290-300, 290-300. . (b)(b) after Pearce (1982) after Pearce (1982) in Thorpe (ed.),in Thorpe (ed.),Andesites: Orogenic andesites and related rocks. Wiley. Andesites: Orogenic andesites and related rocks. Wiley. ChichesterChichester. pp. 525-548. pp. 525-548, , Coish Coish et al. (1986), et al. (1986), Amer. J. Sci., Amer. J. Sci., 286286, 1-28, 1-28.. (c)(c)after Mullen (1983), after Mullen (1983), Earth Planet. Sci. Earth Planet. Sci. LettLett., ., 6262, 53-62., 53-62.